If it's a kid's computer, odds are there is a lot of
"JUNK."
First: To clean house, use Disk Cleanup in Windows, which purges temp files, downloaded programs, setup logs, and the Recycle Bin, in addition to compressing many unused files so that they take up less room. Your computer will breathe a big sigh of relief after you do this. (To find Disk Cleanup, go from the Start menu to Control Panel,/System and Security/ Administrative Tools/Free up Disk Space.
Then in the same area: go from the Start menu to Control Panel,/System and Security/ Administrative Tools/Defragment your Hard Drive
Also, consider downloading and running the free version of what used to be called "Crap Cleaner."
https://www.piriform.com/ccleaner
Finally, if your kids are like mine:
There are almost certainly multiple programs running in the background of your computer without your knowledge or permission. I am sure (I HOPE) you are using an antivirus program, but you should also:
Download a program called Malwarebytes.
www.malwarebytes.org
You only need the free version. Let the program upgrade every time it runs, to make sure it’s up to date. Once you’re all set, click the Scan tab and then Scan Now. You don’t want any of the junk found by the spyware scanners, so check all the checkboxes and click “Remove.” Do this every couple of weeks, depending on how much web surfing you’ve been doing.
There are other things you can do, but do these and see if they help.
Oh, if there is a ton of music and photos stored on the computer, take it off. Put it on a flash drive or something and then delete from the laptop. Documents don't take much space, but music and photos eat it up...